GLOW WORM, GLOW!

Lesson Objectives:

View cave biomes from ecological and biological perspectives

Relate an organism’s adaptations to its surrounding habitat

Explain the transfer of energy between organisms in an ecosystem

Introduction

The term “glowworm” refers to many different types of flies and beetles that, in their larval and
sometimes adult stages, generate their own glow. There are three primary types of glowworms.
The first are fireflies, a favorite of nighttime porch sitters and children, who like to collect them
in jars. The second group, from the family Phengodidae, are found in North and South America.
Finally, there is the Arachnocampa genus, located in sheltered forest areas, grottos, and caves
in New Zealand and Australia.

These insects glow for different reasons. Adult females seem to glow primarily to attract mates.
Fireflies are thought to glow as a warning signal, visually telling onlookers not to eat them
because they are mildly poisonous. Arachnocampa larvae glow as part of a clever technique for
hunting prey.

Unique Behaviors

Glowworms glow through bioluminescence. This is a chemical reaction that involves a waste
product called luciferin; an enzyme called luciferase acts upon luciferin, as well as the energy
molecule adenosine triphosphate and oxygen. This chemical soup is the recipe for glowing.
Organs in the insect’s abdomen process the mixture. Oxygen levels canbe modified, allowing
the glowworm to turn the light on and off, and to vary its intensity.

Arachnocampa glowworms are actually in their second life cycle. They begin as eggs that are
laid right on cave walls. After three weeks, these eggs hatch to produce tiny larvae that glow
practically upon birth. These larvae continue to grow over a period of several months until they
reach just over an inch in length. It is during this stage that most of the silken thread production
occurs. During the third life stage, the larvae shrink to become translucent. A pupa develops
that suspends from the cave wall. After twelve days, the pupa develops into an adult fly. The
flies only live for a short time, as their main purpose is to mate, lay eggs and initiate the life
cycle.

Status and Conservation Efforts

Accurate population estimates of cave glowworms have been hampered by many of the
insects’ dark, remote habitats. Sometimes a species will only be found in a single spot in the
entire world. In recent years, a colony of an Arachnocampa subspecies was found in a cave on
Mount Buffalo in Victoria, Australia. The Victorian government now recognizes it as a threatened
species.